The ornamental design for a chimneycap, as shown and described.
FIG. 1 is a perspective view of my design showing my chimney cap designs;
FIG. 2 is a front view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof; and the back view would be a mirror image of the front view, and the right side view would be a mirror image of the left side view.